LS 8-18 alpine CFIT after right-turn 360s near ridge; cause undetermined

An experienced alpine pilot (3216 h, >2300 h on type) launched from Bad Ragaz and used thermals along the alpine ridges. In the last minute of GPS recording the LS 8-18 flew two right-hand 360° turns at nearly constant altitude (IAS ~86 km/h, ~10% above stall). The right winglet struck a rock face at ~2680 m AMSL; the outer wing separated and the wreckage slid ~130 m down a scree slope. CAVOK; no defects; no medical impairment. Probable CFIT in controlled flight; the investigation could not determine how it occurred. Aircraft destroyed; pilot fatal.

1. Cruise from Bad Ragaz: Aerotow launch 12:17 from Bad Ragaz (LSZE) rwy 30 for a private cross-country soaring flight without specific goal. Released at 2545 m AMSL near Vilan after 11 min. Used thermals on Schesaplana / Sulzfluh / Madrisa at 2400–2900 m AMSL. CAVOK, 240° at 5 kt, vis >70 km. Glide-back to LSZE remained within reach.
2. Highly experienced mountain pilot: Pilot ~3216 h total / >2300 h on type (LS 8-18). Licensed 1996 at age 41. Mountain soaring expert; routinely launched from Bad Ragaz for alpine cross-country. Last dual check-flight Feb 2017. Already 24 OLC-published flights in 2017.
3. Two right 360s at constant altitude: At 14:38 thermalled SW of Pischahorn for ~10 min (~80 m gained), observed by a paraglider pilot. Continued SSE. In the last minute of GPS recording, flew two right-hand full 360° turns at nearly constant altitude.
4. IAS 10% above stall: In the 20 s before the last data point at 14:50:08, indicated airspeed ~86 km/h — about 10% above the relevant stall speed. Stall scenario considered and judged unlikely.
5. Right winglet strikes rock face: Right winglet contacted rocky terrain at ~2680 m AMSL (estimated ~6 s after the last GPS data point). Wreckage distribution suggests near-vertical impact relative to slope.
6. Outer wing separates; wreckage slides: Right outer wing parted from inner wing at winglet impact. Main wreckage came to rest on a scree slope ~130 m lower (~2550 m AMSL). Pilot fatally injured at primary impact in cockpit; seatbelt rotary lock opened later during the 130 m wreckage slide, ejecting the deceased pilot from the cockpit.
7. Probable CFIT; cause undetermined: Probable controlled flight into terrain (CFIT) shortly after the last GPS data point. No technical defects, no medical impairment, no weather factor. The investigation could not conclusively determine how the controlled flight came to collide with terrain.